Title your presentation “Noon Conference”
Prevents inadvertently giving away the case.
T cells stimulate B cells to produce IgG1 or IgG3 antibodies against acetylcholine receptor (AchR), muscle specific receptor kinase (MuSK), or other protein in Ach pathway
Ice pack test- based on the physiologic principle that neuromuscular transmission improves at lower muscle temperatures. In patients with myasthenia, ptosis can be overcome by direct cooling of the eyelid muscles, positive in our patient
Edrophonium – no longer commercially available in North America
Sero-neg MG- patients thought to have low-affinity/clustered acetylcholine receptor antibodies, Anti-LRP4, Anti-striated muscle antibodies, cortactin, other Abs not detectable by standard panels etc.
RNS- more frequently used because it is more widely available, but less sensitive
Recording electrode placed over the endplate of a muscle, then motor nerve to that muscle is stimulated repeatedly 6 to 10 times, compound muscle action potential (CMAP) amplitude is recorded
Positive if the decrease in CMAP amplitude >10% from initial CMAP
Distal muscles sensitive than proximal
SFEMG- “gold standard”, most sensitive, but more invasive, time consuming, and technically demanding
Patient voluntarily contracts muscle, needle with special electrode is inserted
Measures “jitter”, variability in the latency of each response when single muscle fiber stimulated repeatedly
Increased jitter/variability = positive test
Repetitive stimulation of thoracic nerve in myasthenia patient with respiratory compromise (upper) and healthy control (lower panel)
NIF or NIF worse than 20 cm H2O and FVC less than 10 to 15 mL/kg should prompt intubation
Few RCTs to guide treatment
Pyridostigmine - rapid onset of action (15 to 30 minutes), starting dose 30 mg TID, max dose 120 mg Q4H
Approximately 10%–15% of patients will have evidence for thymoma on chest CT and benefit from thymectomy, but the role of thymectomy in nonthymomatous MG is unclear
Answer: C, 15-30min
Answer: A- MG predominantly affects upper>lower, lambert eaton more often presents with leg>arm weakness
Amifampridine- potassium channel blocker that significantly prolongs the presynaptic nerve terminal membrane depolarization, which enhances calcium entry and thereby improves the release of acetylcholine
